This invention relates to friction welding and, more specifically, to friction welding of one or more structural members to form a structural assembly.
Structural devices are often formed as assemblies of a number of smaller structural members. Such assembling of individual members may be necessary to form devices that are too large or too complicated to be formed by conventional manufacturing methods. For example, such factors as casting sizes, forging sizes, available plate and block sizes, and the like can limit the size and geometry of the structural members that can be manufactured. To form larger or more complex devices, the structural members are typically assembled by joining the individual structural members using a variety of known joining techniques including, for example, mechanical fastening or welding.
Joints formed by mechanical fasteners such as rivets, screws, and bolts typically require an overlap of the structural materials at the joint. The fasteners and the overlap of material result in an increase in weight of the joint and the structural assembly. The joint can also introduce areas of increased stress, for example, around holes drilled for receiving rivets. Alternatively, weld joints can be formed to join the structural members, sometimes requiring little or no overlap of material. However, the formation of conventional weld joints, such as by arc or electron beam welding, can result in undesirable dimensional changes in the structural members. Welding can also introduce porosity or other discontinuities into the structural members or otherwise cause unwanted changes to the material properties of the structural members.
Friction welding has also been proposed as an alternative to conventional welding methods for joining members. Linear friction welding, and rotational friction welding can be used to form strong joints without reducing the mechanical characteristics of the joined materials or causing significant dimensional changes. However, each of these conventional friction welding techniques is limited by the dimensions of the structural members and/or the joints to be formed. For example, conventional linear friction welding and rotational friction welding require one member to be moved, i.e. oscillated or rotated, and urged against the other member. Because of the difficulty of moving large structural members, it can be impossible or impractical to join some structural members by these techniques.
Thus, there exists a need for an improved apparatus and method of joining structural members to form structural assemblies. Preferably, the method should enable the manufacture of preforms that approximate the desired dimensions and configuration of the structural assembly and therefore require little machining or other subsequent processing to form the structural assemblies. The method should be adaptable for joining large and/or complex structural members. Further, the method should not add significant weight to the structural assembly, and should minimize dimensional changes and undesirable changes to the material properties of the structural members.
The present invention provides an apparatus and method for joining structural members to form preforms and structural assemblies. A joining member, which can be smaller than the structural members, is friction welded to join the structural members. The structural members can remain stationary during the joining process and can be large or complex. The friction welding process provides a strong joint without appreciably detracting from the dimensional or material characteristics of the members. Further, the joint can be formed without an overlap of material or other undue additions of weight.
According to one embodiment of the invention, first and second structural members are positioned proximately so that first and second joining surfaces define an angled aperture between the members. In other embodiments, more than two structural members can be positioned to define the aperture so that at least three members are joined. The aperture can be a slot that extends generally uniformly through the members or a frustoconical aperture. A joining member is urged into the slot and against the joining surfaces and moved relative to the members to friction weld the joining member thereto. For example, the structural members can be disposed substantially within a plane and the joining member can be urged in a normal direction generally perpendicular to the plane. The joining member can be moved alternately in first and second opposed directions that are generally parallel to a lengthwise direction of the slot. Alternatively, the joining member can be rotated about an axis generally collinear with a longitudinal axis of the aperture.
According to one aspect of the invention, each structural member defines a clamping portion that extends from the respective structural member and defines a clamping surface, which can be generally parallel to the direction of urging of the joining member. The clamping portions can be inserted in a clamping channel of a clamping device so that the clamping device contacts the clamping surfaces to prevent the aperture from opening while the joining member is urged against the joining surfaces. A space can be provided between the clamping device and the joining member to receive flash from the joining member and the joining surfaces. Additional structural members can also be friction welded to the first and second structural members to maintain their relative positions and prevent the aperture from opening. According to another aspect, the structural members include alignment portions that are engaged to define an interface.
The joining member can be urged against the structural members after the motion of the joining member is terminated to form friction weld joints between the joining surfaces and the joining member as the joining surfaces and the joining members cool. Further, the clamping portion and/or gripping portions can be trimmed from the structural and joining members.
The present invention also provides a preform for use in forming a structural assembly of predetermined dimensions. The preform includes first and second structural members, which can be formed of aluminum, aluminum alloys, titanium, titanium alloys, steel, nickel-based alloys, copper-based alloys, or beryllium-based alloys. Each of the structural members can be formed of the same or different materials, such that the preforms and structural members formed according to the invention can comprise a single or multiple materials. The structural members define joining surfaces, which define an angle therebetween. A joining member corresponding to the angle is disposed between the joining surfaces and joined by friction weld joints to the joining surfaces. Each structural member also defines a clamping portion that extends from the respective structural member. The clamping portions define generally parallel clamping surfaces for engaging an aperture of a clamping device. According to one aspect of the invention, the joining member defines a generally frustoconical plug and the joining surfaces define a generally frustoconical contour corresponding to the joining member. Alternatively, the joining member can define an elongate member and the joining surfaces can define an angled slot that extends generally uniformly in a lengthwise direction of the joining member and corresponds to the joining member.
According to another aspect of the invention, the structural members define alignment portions that are engaged to define an interface therebetween. A space between the interface of the alignment portions and the joining member can be at least partially filled with flash from the joining member and/or the joining surfaces. The joining member can also include a gripping portion that extends from between the first and second structural members.
According to another embodiment, the present invention provides a structural assembly that is formed from the described preform by trimming the clamping portions of the structural members and the gripping portion of the joining member.
The present invention also provides an apparatus for joining at least two structural members to form a structural assembly. The apparatus includes a clamping device that defines a clamping aperture for receiving at least a portion of the structural members so that the structural members define an angled aperture for receiving a joining member. A connection device, configured to be connected to a joining member, is actuated by first and second actuators. The first actuator is configured to urge the connection device toward the clamping device and thereby urge the joining member into the angled aperture between the structural members. The second actuator is configured to move the connection device and thereby friction weld the joining member to the structural members. The clamping device is structured to engage a clamping surface of each structural member to restrain the structural members and thereby prevent the angled aperture from opening. The angled aperture can be a slot, and the second actuator can be configured to move the connection device in first and second opposed directions generally parallel to a lengthwise direction of the slot to friction weld the joining member to the structural members. Alternatively, the aperture can be a generally frustoconical aperture, and the second actuator can be configured to rotate the connection device about an axis generally collinear to the aperture to friction weld the joining member to the structural members. The clamping device can also define a space in the angled aperture for receiving flash from the joining member while the joining member is being joined to the structural members.